1. Field
The present invention relates generally to a method for a combined active and passive leg prosthesis system and a combined active and passive leg prosthesis system for replacing a missing lower extremity of an individual to perform a gait cycle (take a step) by the leg prosthesis system. The leg prosthesis system has at least one movable joint and a drive unit to drive the movable joint.
More specifically, the present invention concerns a leg prosthesis system intended for a person who has a leg amputated above or below the knee joint. Thus the system may comprise an articulated ankle joint or both an articulated knee joint and an articulated ankle joint.
2. Description of the Related Art
A leg prosthesis system of the type stated above can be adjusted and used by wearers of a prosthesis at different amputation levels.
A person uses his entire body to perform a movement. A gait cycle, that is two steps, is divided into a support phase and a swing phase. The support phase is when the foot of the leg is in contact with the ground, and during the swing phase the foot swings freely in the air. In walking, one leg swings forward with a flexion in hip, knee and ankle joint while at the same time the arm on the opposite side swings forward. The arm on the same side swings backward and helps to increase the forward force and promotes balance. When the foot of the leg touches the ground, heel touching ground, the weight of the body is supported and the forward fall is braked. The leg supports the body and drives it forward until the next leg takes over in placing the heel on the ground.
If one or more joints and muscles are missing, in this case in lower extremities, there will be imbalance and more energy will be consumed. The more joints that are missing and the higher the amputation level, the more energy is required to perform a gait cycle.
A gait cycle, in this case for a leg prosthesis system, can be identified as the movement performed by leg prosthesis system from placing the heel on the ground to the next placing of the heel on the ground with the same leg.
A leg prosthesis system according to the invention can be used to facilitate different types of gait cycles for the prosthesis wearer, for instance to walk at varying speeds, to climb or descend stairs or walk on inclined surfaces.
With the leg prostheses that are available on the market, it is difficult or even impossible for a leg prosthesis wearer to perform certain types of gait cycles.
The leg prosthesis systems that are being sold today are completely passive, that is no external energy is supplied to the prosthesis in addition to the prosthesis wearer's kinetic energy. A passive prosthesis can only lock, dampen and decelerate a movement. With a good passive leg prosthesis system according to prior art technique, a prosthesis wearer can handle most everyday situations, such as sit down, stand, walk on flat ground and descend stairs and slopes.
However, the energy that can be supplied to a passive leg prosthesis system by the prosthesis wearer is in most cases not sufficient to perform more energy-consuming gait cycles, such as stand up from a sitting position, quick increase of speed or climb a staircase or a steep slope. Another problem is to ensure ground clearance to reduce the risk of stumbling.
The manufacture and development of active leg prosthesis systems has only started recently, that is prostheses comprising motors and power sources. By supply of power, the leg prosthesis system helps the prosthesis wearer to perform certain gait cycles such as climb a staircase.
The technique chosen to supply power in active leg prosthesis systems, according to prior art technique, has resulted in problems, such as high movement of inertia in moving the movable joints of the leg prosthesis system. All parts have to be driven when performing a gait cycle and the energy consumption in the leg prosthesis system will be high.
There is thus a need to improve prior art and many of the leg prostheses that are currently available on the market.